Process of polymerizing conjugated diolefins by contacting same with a catalyst comprising a complex of a lithium hydrocarbon with a ferrocene



United States Patent ABSTRACT OF THE DISCLOSURE Conjugated diolefins arepolymerized in the presence of catalysts comprising compounds of theformula Hio-m-n U in 1 I (hydrocarbon) m m is an integer from 0 to 3 nis an integer from 1 to (8m) and (hydrocarbon) indicates a hydrocarbongroup containing up to 10 carbon atoms wherein The resulting polymersare characterized by excellent green strength and building tack, broadmolecular weight distribution, high cis-1,4 structure, desirablemicrogel content, and by the excellent properties of vulcanizates madetherefrom.

This invention relates to the polymerization of conjugated diolefins.

In recent years there have been developed processes for thepolymerization of conjugated diolefins using catalysts based uponlithium, i.e., lithium metal or compounds of lithium in which thelithium is sufficiently active to displace hydrogen from water, etg.hydrocarbon lithiums and the like. These catalysts produce polymerswhich !are high in the desirable cis-1,4 structure, and which yieldexcellent rubbery vulcanizates. However, particularly where it isdesired to obtain the highest possible cis-l,4 structure, the catalystsmust be employed in extremely small quantities, which leads todifiiculties of control, since greater or lesser amounts of theunavoidably variable trace impurities in the monomers, solvent and othercomponents of the system will produce a disproportionate disturbance ina low-catalyst system. Likewise the polymers leave something to bedesired in green strength. In unvulcanized state, these polymers tend tolack the mechanical strength requisite for processing and fabricatingoperations necessarily carried out thereon prior to vulcanization.Typically, the maximum stress which the unvulcanized materials willexhibit during deformation is nather low, occurs at an early stage inthe deformation, and, moreover, drops off quite rapidly as thedeformation continues beyond the point at which maximum stress isexhibited. Unvulcanized strips or other preforms are apt to pull aparttaffy'wise during building etc. operations carried out thereon.

Another characteristic in which these polymers leave something to bedesired is the matter of building tack. In the construction of tires andother manufactured articles, it is frequently necessary to assemblecomponents 3,412,079 Patented Nov. 19, 1968 ice of uncured rubberymaterial together, making use of their natural autoadhesion or buildingtack.

The deficiencies of these polymers discussed above appear to beconnected in some way with the narrow molecular weight range and absenceof microgel (gel particles small enough so as not to interfere with theprocessabiilty of the polymers) characteristic of these polymers.

Accordingly it is an object of this invention to provide a novel andimproved process for the polymerization of conjugated diolefins makinguse of lithium catalysis.

Another object is to provide such a process which is readily andreproducibly controllable.

A further object is to provide such a process which will result inpolymers having desirable Igreen strength characteristics,

A further object is to provide such a process which will result inpolymers having good building tack.

A still further object is to provide such a process which will producepolymers having a wider molecular Weight distribution, and an enhancedmicrogel, as compared with polymers of this type heretofore produced.

Synopsis of the invention The above and other objects are secured, inaccordance with this invention, by polymerizing conjugated diolefins, ormixtures therewith with other olefinically unsaturated compoundscopolymerizable therewith, in the presence of a catalyst comprising thereaction product of a lithium hydrocarbon compound with ferrocene in themole ratio of carbon-bound lithium: ferrocene in the range of 1:1 to10:1. The process is much less disturbed by impurities in thepolymerization system, than has been the case with hydrocarbon lithiumand other lithium-based catalysts heretofore employed. The polymericproducts are characterized by excellent green strength and buildingtack, and by desirable fundamental properties, viz. broad molecularWeight distribution, high cis-l,4 structure, and desirable microgelcontent, as well as excellent vucanizate properties after vucanizationby sulfur/accelerators with any of the known vulcanization systems.

The monomers to be polymerized These may be any of the conjugateddiolefins containing up to six carbon atoms, or mixtures thereof witheach other with lesser proportions (say up to 30%, based on the totalweight of monomers) of other unsaturated compounds copolymerizabletherewith. Examples of suitable conjugated diolefins include, forinstance butadiene, isoprene, 2,3-dirnethyl buta-diene, piperylene,1,2-dimethy1 butadiene, and the like. Other monomers which may becopolymerized with the conjugated diolefins include the vinylsubstituted benzenes such as styrene, alpha-methyl styrene, 0-, pandm-methyl and ethyl-substituted styrenes, allene, vinyl naphthalene,acrylonitrile, methacrylonitrile, acrylate esters, rnethacrylate esters,amides, etc. and the like.

These should be used in minor amounts, say not more than 30%, based onthe total weight of the conjugated di olefins and comonomers, so as toleave intact the essential polydiolefin character of the polymericproducts.

The lithium hydrocarbon-ferrocene reaction products These may beprepared by reacting together, in a suitable inert organic medium, ahydrocarbon lithium compound with ferrocene or hydrocarbon-substitutedferrocene in mole ratios of carbon-bound lithium: ferrocene of 1:1 toabout 10:1 and preferably 2:1 to 8:1. The hydrocarbon substitutedferrocene may be any in which the cyclopentadiene rings contain up to 3hydrocarbon groups replacing hydrogens on the rings, each hydrocarbongroup containing up to 10 carbon atoms. Suitable ferrocene-typecompounds for the reaction include for instance ferrocene itself, andhydrocarbon-substituted ferrocenes such as methyl ferrocene, ethylferrocene, octyl ferrocene, bridged ferrocenes such as the indene-ringhomolog of ferrocene, viz. benzoferrocene, methyl ethyl ferrocene,phenyl ferrocene, benzyl ferrocene and the like. Suitable hydrocarbonlithium compounds include, for instance, any hydrocarbons containing upto 40 carbon atoms in which one or more hydrogen atoms have beenreplaced by lithium atoms such as ethyl lithium, butyl lithium, dodecyllithium, tetramethylene dilithium, pentamethylene dilithium, phenyllithium, benzyl lithium, and the like. The reaction has not been fullyelucidated, but it appears that the lithium in the hydrocarbon lithiumcompound replaces one or more hydrogen atoms of the ferrocene, thehydrogen so displaced combining with the hydrocarbon radical to form thefree hydrocarbon. The reaction may be written thus, for the replacementof a single hydrogen atom by the action of butyl lithium:

C H Li+II Liwficn-rw Fe Fe I'll I'll It will be understood that morethan one hydrogen of the ferrocene may be replaced in this way, up to atotal of about four hydrogen atoms per ring or eight hydrogen atoms forthe entire molecule of ferrocene.

The unsubstituted ferrocene molecule contains ten hydrogen atoms, ofwhich eight may be replaced by lithium. Assuming that m, an integer fromto 3, is the number of hydrogens that have been replaced by hydrocarbongroups, then (8-m) is the number of hydrogens available for replacementby lithium, and 8m=n will be the maximum number of lithium atoms in thefinal reaction product. On this basis, the formula of the reactionproduct is l0mn w n Fe l (hydrocarbon) m m is an integer from 0 to 3 nis an integer from 1 to (8m) wherein and (hydrocarbon indicates ahydrocarbon group containing up to 10 carbon atoms.

The reaction takes place relatively slowly at ordinary temperatures,being completed over the course of several days. The reaction istemperature-dependent and more rapid reactions can be obtained atslightly higher temperatures. The reaction product takes the form of aprecipitate which settles out of the reaction mass. It is understood itwould not be strictly necessary to wait for the completion of thereaction; the precipitated reaction product begins to form almost atonce, and can be removed and used as a catalyst even though theremainder of the reaction mixture has not reacted. Generally, thereaction is carried out at temperatures in the range of to 100? C. Itwill usually be most convenient to allow the reaction to go tocompletion, so that no unreacted butyl lithium remains in solution, andto use the whole preparation as a catalyst. As noted above, the reactionis carried out in an inert organic solvent, usually in an amount suchthat the ferrocene will constitute from .001% to 75% of the sum of theweights of the solvent and ferrocene. Suitable inert organic solventsare exemplified in hydrocarbons containing up to 40 carbon atoms, orpreferably up to 16 carbon atoms such as paraffins on the order ofpropane, butane, hexane, cyclohexane, methyl cyclohexane, heptane,petroleum ether, kerosene, diesel oil, or the like, or aromatichydrocarbons such as benzene, toluene, the several xylenes, hydrogenatedaromatics such as tetralin, decalin, and the like.

The polymerization procedure The polymerization may be carried out inbulk, in the absence of any solvent, or in solution in a solvent such assuggested above for the preparation of the catalyst. Usually, sufficientpressure is applied to keep the greater part of the conjugated diolefinin the liquid phase, although the polymerization may be carried out withthe conjugated diolefin in the gaseous phase. The polymerization iscarried out by contacting the monomeric material, i.e., the diolefins ormixtures thereof together with any monomers to be copolymerized therein,either in bulk or in solution in a solvent, with the catalyst preparedas described above, at temperatures on the order of 20 C. to +150 C.,preferably +25 C. to C.

As to the amount of catalyst to be used, in general, the larger theamount of catalyst used, the more rapidly the polymerization willproceed. Countervailing this desirable effect, high concentrations ofcatalysts tend to lower the molecular weight of the polymers and alsoalter the microstructure of the polymeric chains. Based on theseconsiderations, the amount of catalyst employed should be such as tocontain not more than 0.1 gram, and preferably not more than 0.02 gram,of carbon-linked lithium, expressed as metallic lithium, per grams ofisoprene in the polymerization mixture. There appears to be notheoretical lower limit to the amount of catalyst used; at lowconcentrations, the catalysts appear to have a high order of efficiency,i.e., if the reaction environment is scrupulously purged of allcontaiminants such as oxygen, ozone, water, carbon dioxide, etc., whichwould react with and consume the catalyst, the catalyst appears to beused princapally in the production of polymer chains so that, as long asany catalyst is present, some degree of polymerization will take place.For economic reasons of obtaining a rapid reaction rate and optimumreactor utilization, it is preferred to have at least 0.00002 gram ofcarbonbonded lithium present per 100 grams of isoprene. The aboveconcentrations are, of course, expressed on the basis of catalystefi'ectively present in the polymerization mass; if substances whichwill react with and destroy the catalyst are permitted to enter thereaction zone, the amount of catalyst so destroyed must be subtractedfrom that supplied in applying the above criteria.

For the purpose of establishing the effective concentration ofcarbon-linked lithium in any catalyst preparation employed in thepractice of this invention, the differential titration technique ofGilman and Haubein J. Am. Chem. Soc. 66; 1515 (1944) has been found themost suitable procedure, and the concentrations referred to hereinaboveand in the claims are to be applied on the basis of analyses made bythis method, if any question arises on this point. For most practicalpurposes, where side reactions are not suspected, simple titration withacid will give reasonably accurate results.

The monomeric material may be dissolved in any of the solvents mentionedabove as suitable vehicles for the preparation of the catalyst itself.The concentration of monomers is most conveniently kept in the range of3 to 15% by weight of the entire polymerization mass, as the materialsare most readily handled in this range. However, this is not critical,and higher or lower concentrations may be employed. The systempreferably should be kept free as possible from oxygen and/or oxygenatedor nitrogenous compounds such as water, ethers, ketones, esters, aminesand the like, as these compounds tend to react with and destroy thecatalyst, and if present in amounts in exces stoichiometrically inrelation to the catalyst, will increasingly diminish the cis-1,4configuration of the polymeric products. The polymerization should becarried out in such a manner as to insure thorough cont-act of thecatalyst and monomers, and effective removal of heat; for instance, withsmall scale operations, in glass bottles which are tumbled, at leastinitially to effect mixing; or on a large scale, in autoclaves providedwith rotary agitators and cooling jackets. After the polymerization hasproceeded to the desired extent, the polymer may be recovered from thesolution by any suitable means, for instance my injection into hotwater, which will flash off the solvent or any unreacted monomers,leaving the polymer as crumbs dispersed in the water; or by drying on adrum or extruder dryer; or by mixing the solution with a non-solvent forthe polymer, such as methanol, isopropyl alcohol or the like toprecipitate the polymer.

One of the advantages of the present invention is its lesser sensitivityto variations in catalyst concentration, and to impurities in thesystem. In order to secure optimum polymer structure and desirablemolecular weight, it is necessary, with the simple hydrocarbon lithiumcatalysts, to employ these in very low concentrations, at whichconcentrations small amounts of impurities exert a disproportionatedestructive and/or modifying action thereon. The present catalysts maybe used in larger amounts to achieve the same excellent polymerproperties and are, moreover, less sensitive to impurities; and a lessscrupulous control and monitoring of catalyst concentrations in relationto monomer and solvent impurities may be observed without undulyaffecting the process and product.

T he polymeric products The products of the process of the invention arecharacterized by high and reproducible molecular weight, and excellentmicrostructure, in optimum cases having cis-1,4- contents, as reflectedby infra-red measurements, on the order of 94.0+%. Moreover the productsappear to be characterized by lesser amounts of unidentifiablestructures, as reflected by higher values for total found figuresobtained on such measurements. The products also appear to have a widerdispersion of molecular weights, as compared to polymers hithertoprepared from lithiumbased catalysts. These differences in fundamentalstructure are reflected in the improved technical properties of theproducts of this invention. Earlier polymers have been somewhatdeficient in building tack, i.e., self-adhesiveness in the unvulcanizedstate which enables plies of the polymers to be built up into uncuredpreforms; and in green strengthupon the deformation of the unvulcanizedmaterials, the stress increases up to a certain point, the maximumstress, at a rather early point in the deformation, and thereafterdecays rapidly upon further deformation. The polymers produced inaccordance with the present invention have much improved tack, andexhibit a much improved unvulcanized green strength, in comparison withprevious lithium polymers.

Evaluation of the polymers In the examples hereinafter, various analysesand tests are conducted upon the polymeric products to determine thecis-1,4, trans-1,4, 1,2- and 3,4-structures in the polymer. With regardto the infra-red analyses, the relative amounts of the four structuresnamed are found by measuring the intensities of the infra-red absorptionbands at 8.85, 8.68, 10.98 and 11.25 microns for the four types ofstructures, in the order given above, and inserting these values intothe equation:

D absorbance (optical density) of the polymer at wavelength i e =theabsorptivitives of the several structures at wavelength i, thesubscripts 1, 2, 3 or 4 referring to the several component structuresand C or =the concentrations of the several structures, the subscripts1,2,3 or 4 referring to the several component structures.

The four equations obtained in this way were solved for C C C and C thevalues of the concentrations of the cis-1,4-, trans-1,4-; 1,2-additionand 3,4-addition of the polymer.

The peak wavelengths selected, and the values of the absorptivities efor these wavelengths for the several structures, are tabulatedherewith:

Molar Absorptivities a at Wavelength of 8. 68 8. 10.98 11.25 micronsmicrons microns microns In the detailed examples given hereinafter,percentage values are given for the various types of unsaturation. Theseare derived by dividing the absolute concentration of each type ofunsaturation by the sum of the concentrations of the four types ofunsaturation (1,2-; 3,4-; cisand trans-) determined, and multiplying byso that the sum of the percentages given will always be 100%. In orderto assess the accuracy of the determintion, a further figure is given,namely total unsaturation found, hereinafter abbreviated T.F. This isthe quotient of the sum of the concentrations of the various types ofunsaturation found by infra-red analysis, divided by the theoreticalconcentration of all unsaturation which should be present in the sample,assuming, for example, that the polyisoprene is constituted solely ofGel and dilute solution viscosity were also determined as follows.

Determination of gel and dilute solution viscosity (hereinafterabbreviated DSV) on polybutadiene and polyisoprene polymers Apparatus(a) ml. flasks (b) GP or redistilled toluene (c) 5, 10, 25 and 50 ml.pipettes and 100 ml. graduates (d) 100 mesh, conical, steel screens,aluminum cups, and

Reeve Angel filter paper, No. 802

(e) Constant temperature bath equipped with a thermometer reading totenths of a degree and a stirrer (f) A timer reading to tenths of :asecond (g) A No. 50 Ostwald viscometer.

Procedure (a) If the dilute solution viscosity is thought to be around6.0-7.0 or lower, accurately weigh 0.4000 g. polymer. If the dilutesolution viscosity is thought to be 6.0 7.0 or higher, accurately weigh0.2000 g. polymer. The polymer should be unmilled and finely cut. Placethe sample in a 125 ml. Erlenmeyer flask and cover with exactly 100 ml.CR or redistilled toluene which contains 0.0075 g. phenylbeta-naphthylamine per liter. Swirl gently to separate the Particles.

(b) Set the flask in a dark place. Several hours later swirl again toremove polymer from the bottom of the flask. T wenty-four hours latershake again making sure all the polymer is removed from the bottom ofthe flask. A neoprene policeman may be necessary to accomplish this.Take care that no polymer remains on the policeman. Allow to stand forabout .an 'hour.

(c) Filter the liquid through a screen and/or the filter paper dependingupon the gel present. Weigh an aluminum (d) Pipette a ml. aliquot of thefiltered solution into the aluminum cup and evaporate to dryness on ahot plate at 100 C.1l0 C. Place in a hot air oven at 100 C. for an hour.Cool for a few minutes and weigh. This weight will be needed tocalculate gel content and dilute one-inch wide strip, together with itsliner, was cut out and wrapped and secured around the cylinder, rubberside out. A similar strip was cut out and wrapped around the firststrip, with the rubber faces in contact and a tail of the strip hangingfree. This tail was attached to the lower jaw of the testing machine.The machine was then set in operation, with the lower jaw retreatingfrom the upper at a rate of two inches per minute. The maximum tensileforce, in pounds, shown on the measuring head was recorded as thebuilding tack of the compound.

solution viscosity. 10 With the foregoing general discussion in mind,there (e) For dilute solution viscosity, adjust the constant are givenherewith detailed specific examples of the exectemperature bath to 25'C. '-0.1 C. ution of this invention.

(f) Rinse a clean No. 50 Ostwald viscometer two or three times with C.P.or redistilled toluene to which has Preparanon of Catalyst been added0.0075 g. phenyl beta-naphthylamine per liter. zene 300 ml. Drain theviscometer as dry as possible without the use of (distilled over sodium)a Vacuum line and place in the constant temperature bath. Fe rocene g.(0.1 mol). Pipette 5 ml. of toluene plus phenyl beta-naphthylamine Butyllithium solution (in heptane, into the large arm of the Ostwaldviscometer. 20 containing .011368 g. of lithium (g) Draw the solventabove the second blue mark on per ml.) 250 ml, the small arm of theviscometer. Measure the time it takes (0.4 mol of Li). {the solvent to qbetween the two marks on The above ingredients were charged into a32-ounce 2:;- The flow tune of two runs Should check Wlthm beveragebottle, which was then flushed with argon, and sealed with aneoprene-lined crown cap provided with a (h) Dllut? the Polymer 9 i acnCentrat1iOn.s perforation for withdrawal of the contents by hypodermicthat the of the flow tune. of It 6 polymer g syringe. The bottle wasswirled to mix the contents and the flow tune 0f.the solvent 13 bitweenn placed in a water bath at 70 C. for 6 days. During the hlgh molecularweight polymers t cggcentra Ion g course of this time a precipitateformed which was readily have to bg i as 0'0150 m e i i re-suspendibleby shaking the bottle. An analysis of the gi ig i g?22 if; i zgifig g gbgg mt e m suspension showed .00254 gram-atom of carbon-bound lithiumper ml. and .00461 total alkalinity per ml., cal- (1) Plpette abolit 5of the polymer Into the culated as gram-atoms of lithium. Thissuspension was large arm of the viscometer. Draw the solution up throughused as the Catal yst 1n the polymerizatlon experiments to the capillaryto rinse out the solvent. Drain the viscomfollow and will hereinafter bedsi Hated c t 1 t eter. Pipette 5 ml. of the polymer solution into theviscomensioil A g a a Y eter and measure the flow time as describedabove. p

Information needed for calculation of gel and EXAMPLE POLYMERIZATIONdilute solution viscosity 40 isoprene Ca 200 g., per Table I. a 3 5 5 or0'4000 Catalyst suspension A 12 or 13 m], 3. Weight of aluminum cup andresidue of 10 ml. aliquot Per Table of polymer solution Two runs weremade in accordance with the foregoing 4. Concentration of dilute polymersolution in g./ 100 ml. recipe. In each run a tared 28-ounce beveragebottle 5. Flow time in seconds of the solvent Was baked at 250 C. for 24hours, then cooled while 6. Flow time in seconds of the solutionflushing with nitrtohgen. The bottles were then filled with isoprene,and, wi continued nitrogen flushing, warmed Calculanons Involved on asand bath to boil ofli a large portion of the isoprene Original Wt.-10so as to insure removal of all dissolved nitrogen. The Gel: of f l 0fpolymfil solutlonx 100 bottle was then capped with a perforated,neoprene-lined Original Wt. crown cap, and hypodermically pressurizedwith nitrogen. Dilute S i Vi it Tjli'ie bottle was then re-weighed todetermine the amount o isoprene t erein. The bottle was then cooled to 0C., 2 303 10 (12221 3 1 5 f g opened briefly to inject the catalyst,re-pressurized, and econ S 0 so ven re-sealed with a silver-lined crowncap. The bottle was concentmmon 1n g-/1OO then swirled to mix thecontents, and kept in a polymer- Values for building tack givenhereinbelow were ization box at 8 C. for a duration of time indicatedfor determined as follows. There was provided a cylinder two the run inTable I. At the end of this time, the bottle inches in diameter by twoinches in length mounted to was cut open and the contents dumped intomethanol rotate to the upper, tension-measuring, head of a tensilecontaining 1% of phenyl-beta-naphthylamine. The polytesting machine(lnstron Model TTG), The nv l a mer was then dried in a vacuum oven. Setforth herewith ized composition to be tested was sheeted out to athickin Table I are particulars of the runs and properties of ness of &inch, and placed on a holland cloth liner. A the products.

TABLE I Isoprene Catalyst i ai t i riif Conversion Propemes of ProductRun No. (grams) suspglnston Else (percent) sv (pegglnt) Infra-redAnalysis (percent) Cis-1,4 Trans-1,4 1,2- 3,4- 'IF $111111: 3%? i5 33it? it? 3 32.; 3:3 358 5 53 33.? a 200 12 24 19.5 16.1 0 94.1 0.0 0.05.9 90.5 4 200 16 24 7.4 0 93.) 0.0 0,0 ,1 901 In thisrun,aitcrsealinginthe eatalystwas quicklydroppcdintoabucket of water at about 15 0., andallowed to react; to

about 20% conversion. The bottle was then transferred to a water bath at24 C. to complete the polymerization.

TAB LE 111 Ml. of Yield Gel Infra-red Analysis (percent) Run No CatalystDSV (percent) Grams Percent Cis-1.4 Trans-1,4 1,2- T. F.

EXAMPLE V (hydrocarbon) indicates a hydrocarbon group containing Hexanegrams 87 6 up to 10 carbon 'atoms Butadiene grams 33 1 1O 2. Processaccording to claim 1, wherein the monocatalyst fi,i fb' 6 O mericsubstance is isoprene.

The above ingredients were charged into a polymerization bottle asdescribed in Example III. The bottle was then placed in a polymerizationcabinet at 50 C. for 21 hours, and the polymer recovered as described inExample I. There were recovered 30.2 grams (91.2% conversion) of apolymer having a DSV of 6.59 and exhibiting, by infra-red analysis,45.1% cis-1,4, 47.2% trans-1,4 and 7.7% 1,2-unsaturation, the totalfound being 95.8%.

From the foregoing general discussion and detailed specific experimentalexamples, it will be seen that this invention provides a novel processfor the polymerization of conjugated diolefins to yield products ofimproved microstructure and physical properties, particularly greenstrength and tack. The process is more readily controllable andreproducible than earlier processes based upon lithium compoundcatalysts, and the reactants employed are inexpensive and readilyavailable.

What is claimed is:

1. Process of polymerizing a monomeric substance selected from the groupconsisting of conjugated diolefins containing up to six carbon atoms andmixtures thereof with each other and with up to based on the weight ofthe monomeric substance, of other unsaturated compounds copolymerizabletherewith, which comprises contacting the same with a catalystcomprising a compound of the formula (hydrocarbon)...

wherein m is an integer from 0 to 3 n is an integer from 1 to (8-m) and3. Process according to claim 1, wherein the monomeric substance isbutadiene.

4. Process according to claim 1, wherein M 0 and n is greater than 2.

5. A catalytic composition comprising a compound of the formula 6.Process according to claim 1 wherein the catalytic compound has theformula Ha I References Cited UNITED STATES PATENTS 8/1966 Forman, etal. 26094.2

OTHER REFERENCES JOSEPH L. SCHOFER, Primary Examiner.

R. A. GAITHER, Assistant Examiner.

